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Old 4th June 2009, 10:21 PM   #21
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Quote:
By bigun - Let's see if this works... attaching the spice file
It not only works , but it works while it oscillates (attached). That was with the "slower" MJL21193/4. A perfect sub for the RCA is the lowly 2n3055/2955 , this worked perfectly. In fact, with bc556 for LTP, BD's for VAS/drivers , and the slow OPS ... it worked perfectly - nearly the same as mine with the fast devices.

This confirms that the topology is tailored to the devices, not the other way around. As it is , this EXACT circuit will not run fast OP
devices. Conversely , the new one will run slow or fast drivers.
with a 4 ohm load , I could see the OP clip before the rails (VI limiter)
at about 3 A.
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Old 5th June 2009, 12:28 AM   #22
Bigun is offline Bigun  Canada
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Looks good, I think there is a big market for oscillators in many industries

So, the plan is to change the circuit to suit modern devices.

I now have a name for this amplifer: BACK TO THE FUTURE AMP
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Old 5th June 2009, 03:19 AM   #23
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"Uncle charlie" did not lie (DX = .03%), I did the RCA , the DX , and the "back to the future". By "did" I mean simulate with the .step directive in EVERY way to find the best operating points. By accident , I noticed what effect the small cap (100nf)in parallel with the bootstrap on the DX has at HF. IT could be another "secret".

Starting with the RCA (.08-.1) then the DX (.03-.04) and finally the new one, THD dropped with each generation. This has to be the parts , as all the other aspects of operation (open loop gain , phase margin) were nearly the same. As this is my first real in-depth investigation of the "good ol' amp" topology , I was surprised at sub .02% readings.

The current source , while some say it may detract from the sound, improves things. 1. PSRR , a no brainer. 2. keeps the differential balanced independent of supply voltage (25 -45v),and 3. everything remained the same regardless of output level/frequency.
Balance seems to be the key to good sound, H3 ,offset and total THD dropped , but H2 increased slightly at the "sweetspot" (attached - orange plot is the "sweetspot") With a 4R load ,a larger bootstrap capacitor (100u)makes for better performance as well.

What was amazing is that the RCA could simulate , clip and oscillate simultaniously without a timestep error in LT (the bootstrap will not allow RF oscillation? ) .

The only feature that will be "handy" is a trimmable CCS to balance the LTP , otherwise this should sound as good as the "supersym". Both these and the sym's will be in the same amp , so I can swap front and rears with the PC for a good A/B listening test. Time to finish the boards..
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Old 5th June 2009, 03:42 AM   #24
mannycc is offline mannycc  Singapore
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Hi all,
Can somebody explain to me? I'm referring to the circuit input stage posted by OS, i have seen quite a few similar circuits with resistor connected to ground (R27 + diodes) but dont know exactly the purpose, few questions...
1.does it give improvement to sonics, distortion?
2.is it to change the input impedance?
3.is it the one called lifted ground?

Appreciate your feedback.

B.regards,
mannycc
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Old 5th June 2009, 04:15 AM   #25
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1. no
2. no
3. The resistance (10R or 22r) will reduce a ground loop between different components and in case of a real screwup (live chassis or improper house wiring) , break the connection between signal ground and the real ground (physically burn out). The diodes will short out a minor potential between grounds.

With a minor ground loop the circuit will drastically reduce hum.
If the DC feedback cap and other critical small signal grounds of the amp also go to this "lifted ground" ,they also benefit from this technique. You do not connect the rail capacitor grounds to this point.

OS
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Old 5th June 2009, 01:29 PM   #26
Bigun is offline Bigun  Canada
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Quote:
Originally posted by ostripper
"Uncle charlie" did not lie (DX = .03%), I did the RCA , the DX , and the "back to the future". By "did" I mean simulate with the .step directive in EVERY way to find the best operating points. OS
That's a nice piece of sim work. I haven't tried the .step before, usually doing it manually. The TGM uses a larger bootstrap than DX, more like 220uF but 100uF is more common in this position.

I think the comments about current sources not sounding nice applies to current mirrors - they behave differently than the simple current source.
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Old 5th June 2009, 02:37 PM   #27
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Default When i started to make the Dx, i was thinking it would have 0.5% THD


Was a very nice surprise when i learned how to use the analisis into the simulator.

I really do not think good measurements guarantees good performance, may be a nice indications, that it is possible the amplifier sounds fine... i have listen sterile very low distortion units and lovely high distortion units.

Since very young i found that topologie sounding delicious, listening many brands and building several schematics...has a character, a personalitty, some punch on bass and some warm sound... suddenly pretty good recordings shows it can reproduce treble very well too...not my amplifier quality...the topologie quality..all them had that kind of sonics.

Aksa is different, another decision taken into the bass, having 3 db losses into 40 hertz (decisions taken when he made it i think)..and this to the Aksa 55 standard..he made other ones..Nirvana and Nirvana plus.

You see...the Scott sounds almost the same...and hundreds of others made by Sony, JVC, Kenwood, Marantz, Pioneer and all major brands..the circuit is inside several chip amplifiers, from the STK to some Panasonic 4 channel chip amplifier going to some TDA chips too.

If you keep the long tail with resistances.... the differential colector loads using resistances... the traditional simple VAS without emitter resistance.... bootstrapp and emitter follower, not using mirror, current sinks, CCS, voltage regulators, double differential (complementary alike Leach amplifier), if you do not use tripple darlington (sometimes oscilates..oscilations driven by the signal..superimposed to high frequencies)... them you gonna have this style of sound...marvellous sonics...warm feeling sound... strong punch on bass...interesting sound stage..not wide open, not strange or over dimensioned.

I took the care to try almost everything..maybe not all possible combinations because the number is very high..but i have installed CCS into differential..also current sink into the differential collectors, have installed CCS there too, have installed shunts, voltage regulators, double differential, differential VAS, complementary VAS, darlington VAS, Doctor Self style VAS, over current protection into the output...VBE voltage limiters....CCS into the drivers, and other styles of connection into the output, different from the emitter follower.

Those modifications changed the sound character completelly, as produce another topologie..or a modified topologie...one of them resulted into the HRII...other resulted into the Precision...the ones i have appreciated i have made other amplifiers, other models using them...but sounds different..one has middle range..other plays very loud and you be surprised how powerfull it can be (HRII), other is an earthquake (DHR Turbo)..and so on.

There are hundreds of possibilites with the surrounding parts applied to differential, vas and output..and each one of them will sound different.

My prefered sound, to listen in my home, is the Standard....to a party i would use others, to listen voices another one...and so on.

To listen sound stage, then Aksa is unbeatable, as i do not use black gates to bother me.

I have done those testings you are doing..it is fun to do....enjoy yourselves with that...and i hope you find something different i could not find.

All i have made was to try other currents into differential, into VAS, into driver and also into the output as stand by current and to adjust the final one (capacitors and coupling, and levels, and filters) listening and asking help to friends to evaluate by comparison and calling children to listen (they are not politics, have not preference and will protect nobody and no brand)

Was a hard work but easy to make that topologie sound fine..it sounds fine by it's own nature..you can replace all condensers and listen again and it will sound nice (but not the mutant black gates, this is masoquism to use them..people that wants to suffer)

regards,

Carlos
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Old 5th June 2009, 02:52 PM   #28
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Default If Ostripper give me the permission, i will be happy to talk about evaluation


listening tests..what is the method..what is scientific, what is non sense into my point of view.

Not only mine..this is a very old method developed by USA magazines during the seventies.

regards,

Carlos
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Old 5th June 2009, 02:59 PM   #29
Bigun is offline Bigun  Canada
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Carlos,

did you use pretty much the same speakers for a long time ?

If I send you a TGM1 amplifier and you listen to it, will you hear what I hear, because we have different speakers (not only different ears and brain as you say) ?
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Old 5th June 2009, 03:14 PM   #30
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Default Of course...but the test is made by yourself...comparison method


this way you gonna be able, with a fixed speaker, considered reasonable or good, to conclude the amplifier is better.

I mean...it is scientific, by your and me, to say some amplifier is better or tune better than another one, doing a scientifically controled A to B test..a blind test that is something not very easy to do and need a lot of skill to do it.

I hope you know all the steps.

Because i can take two amplifiers..yours and mine..and listen them separatelly, without compare with the same music, same time and same speaker..then i am unable to say the one is better to my taste..... this is already subjective, but entirelly unprecise..one must play followed by the other, same power, same audio source, same music and almost same time..time between one and other cannot be bigger than 1 second.

there's no sound memory...or there's no conditions to evaluate using memory.... this is alike "i think so"...or "it seems to me"..this is not science... a lot of psychological factors enters the judgement....knowing the one you have made..this one gonna be, probable, the winner...because of that blind testing.

I wrote that, tenths of times into the Dx thread...i hope you has this knowledge by yourself, have learned because it is very obvious, or have readed what i have learned with the older folks, more experienced than me, that started that whole thing down the seventies.

Only family is entering, now a days, my mail box... filter applied..a lot of spam and viruses have entered....i have solved the problem but to avoid repeat that stuff i have applied a selective filter to mails to enter.

I would like to know, from you and Ostripper, how old you are folks..sometimes i feel you are very young..sometimes not..can you please inform to your old friend Charlie?

Carlos
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